TROPICAL LAND-USE CHANGE AND SOIL EMISSIONS OF NITROGEN-OXIDES

Increases in the emissions of globally important nitrogen (N) oxide ga ses have coincided with significant changes in land use in the tropics , Clearing of tropical forests and savannas for agriculture currently represents the most extensive alteration of land cover on the planet, Over the last several decades, N fertilizer use has increased globally and in China and the developing world, use has recently surpassed tha t in the developed world. The potential contribution of land-use chang e in the tropics to the increase in N oxides is great, yet only a few studies have measured N oxide emissions after tropical land conversion . Our summary of available research shows some conversions to pastures and a few management practices, especially those using N fertilizers, increase emissions beyond those found in undisturbed ecosystems. Howe ver, not all studies show unequivocal increases in emissions. Accordin gly we call for a mechanistic understanding of the processes controlli ng trace gas fluxes to adequately predict under what conditions increa sed emissions may occur. More measurements are needed to build and tes t models that may improve management of N fertilizer use in tropical a gricultural systems, Given the expected expansion of agriculture and i ncreased use of N fertilizers in the tropics, increased emissions of N oxides from the tropics are likely.